Geraniums are a large group of plants desirable for their bright clusters of flowers, which come in every shade but blue and yellow. The plants vary widely in their sizes and shapes. Some have a trailing habit, some grow best as bedding plants, and many have scented foliage. Geraniums are divided into two groups: Hardy geraniums that can overwinter, and tender plants that are grown as annuals in cold climates.
The water needs of geraniums vary depending on the type and climate. In general, however, all geraniums, including those grown indoors, grow best in soil that is allowed to dry out somewhat. Test the soil by inserting your finger into the dirt. The soil should be dry to a depth of about 4 to 6 inches before you water the plant again. The use of a well-draining soil mixture (choose one that has a large percentage of peat moss, sand or perlite) will also help reduce problems caused by overwatering.
Overwatering your geraniums can lead to serious problems. The soggy soil of indoor geraniums can attract fungus gnats, small insects that thrive on the rotten organic matter present in overly wet soil. Although they don’t present a threat to the life of the plant, the small bugs are a nuisance. A more serious matter that will kill the plant is root rot, which occurs when too-wet soil contributes to the rotting of the plant’s roots. In such cases, the geranium will show an overall decline. The lower leaves will turn yellow and fall off, and the plant will eventually die.
Water at the level of the soil, taking care not to wet the leaves. Water left sitting on the foliage can lead to fungal diseases such as leaf spot. Water until the water freely drains from the bottom of the container, if your geranium is in a pot. If there is a water-catch tray underneath the pot, empty it as soon as the container is done draining. Do not let the pot sit in any water, as this can also lead to root rot.
Geraniums that do not tolerate heat, such as the Martha Washington or hothouse types, may need to be watered once a day during hot summer weather in order to keep the soil moist and cool. This is especially true for container-grown plants, which lose water more quickly than their in-ground counterparts. Hardy geraniums that live through the winter should not be watered when dormant.